Only allow host-relative LDConfig paths

This change only allows host-relative LDConfig paths.

An allow-ldconfig-from-container feature flag is added to allow for this
the default behaviour to be changed.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

internal/config/cli.go

@@ -17,6 +17,7 @@
 package config
 
 import (
+	"fmt"
 	"os"
 	"strings"
 )
@@ -34,29 +35,62 @@ type ContainerCLIConfig struct {
 	NoPivot   bool   `toml:"no-pivot,omitempty"`
 	NoCgroups bool   `toml:"no-cgroups"`
 	User      string `toml:"user"`
-	Ldconfig  string `toml:"ldconfig"`
+	// Ldconfig represents the path to the ldconfig binary to be used to update
+	// the ldcache in a container as it is being created.
+	// If this path starts with a '@' the path is relative to the host and if
+	// not it is treated as a container path.
+	//
+	// Note that the use of container paths are disabled by default and if this
+	// is required, the features.allow-ldconfig-from-container feature gate must
+	// be enabled explicitly.
+	Ldconfig ldconfigPath `toml:"ldconfig"`
 }
 
 // NormalizeLDConfigPath returns the resolved path of the configured LDConfig binary.
 // This is only done for host LDConfigs and is required to handle systems where
 // /sbin/ldconfig is a wrapper around /sbin/ldconfig.real.
 func (c *ContainerCLIConfig) NormalizeLDConfigPath() string {
-	return NormalizeLDConfigPath(c.Ldconfig)
+	return string(c.Ldconfig.normalize())
 }
 
-// NormalizeLDConfigPath returns the resolved path of the configured LDConfig binary.
+// An ldconfigPath is used to represent the path to ldconfig.
+type ldconfigPath string
+
+func (p ldconfigPath) assertValid(allowContainerRelativePath bool) error {
+	if p.isHostRelative() {
+		return nil
+	}
+	if allowContainerRelativePath {
+		return nil
+	}
+	return fmt.Errorf("nvidia-container-cli.ldconfig value %q is not host-relative (does not start with a '@')", p)
+}
+
+func (p ldconfigPath) isHostRelative() bool {
+	return strings.HasPrefix(string(p), "@")
+}
+
+// normalize returns the resolved path of the configured LDConfig binary.
 // This is only done for host LDConfigs and is required to handle systems where
 // /sbin/ldconfig is a wrapper around /sbin/ldconfig.real.
-func NormalizeLDConfigPath(path string) string {
-	if !strings.HasPrefix(path, "@") {
-		return path
+func (p ldconfigPath) normalize() ldconfigPath {
+	if !p.isHostRelative() {
+		return p
 	}
 
+	path := string(p)
 	trimmedPath := strings.TrimSuffix(strings.TrimPrefix(path, "@"), ".real")
 	// If the .real path exists, we return that.
 	if _, err := os.Stat(trimmedPath + ".real"); err == nil {
-		return "@" + trimmedPath + ".real"
+		return ldconfigPath("@" + trimmedPath + ".real")
 	}
 	// If the .real path does not exists (or cannot be read) we return the non-.real path.
-	return "@" + trimmedPath
+	return ldconfigPath("@" + trimmedPath)
+}
+
+// NormalizeLDConfigPath returns the resolved path of the configured LDConfig binary.
+// This is only done for host LDConfigs and is required to handle systems where
+// /sbin/ldconfig is a wrapper around /sbin/ldconfig.real.
+func NormalizeLDConfigPath(path string) string {
+	return string(ldconfigPath(path).normalize())
 }

internal/config/cli_test.go

@@ -33,7 +33,7 @@ func TestNormalizeLDConfigPath(t *testing.T) {
 
 	testCases := []struct {
 		description string
-		ldconfig    string
+		ldconfig    ldconfigPath
 		expected    string
 	}{
 		{
@@ -51,12 +51,12 @@ func TestNormalizeLDConfigPath(t *testing.T) {
 		},
 		{
 			description: "host .real file exists is returned",
-			ldconfig:    "@" + filepath.Join(testDir, "exists.real"),
+			ldconfig:    ldconfigPath("@" + filepath.Join(testDir, "exists.real")),
 			expected:    "@" + filepath.Join(testDir, "exists.real"),
 		},
 		{
 			description: "host resolves .real file",
-			ldconfig:    "@" + filepath.Join(testDir, "exists"),
+			ldconfig:    ldconfigPath("@" + filepath.Join(testDir, "exists")),
 			expected:    "@" + filepath.Join(testDir, "exists.real"),
 		},
 		{

internal/config/config.go

@@ -18,6 +18,7 @@ package config
 
 import (
 	"bufio"
+	"errors"
 	"os"
 	"path/filepath"
 	"strings"
@@ -51,6 +52,8 @@ var (
 	NVIDIAContainerToolkitExecutable = "nvidia-container-toolkit"
 )
 
+var errInvalidConfig = errors.New("invalid config value")
+
 // Config represents the contents of the config.toml file for the NVIDIA Container Toolkit
 // Note: This is currently duplicated by the HookConfig in cmd/nvidia-container-toolkit/hook_config.go
 type Config struct {
@@ -127,8 +130,20 @@ func GetDefault() (*Config, error) {
 	return &d, nil
 }
 
-func getLdConfigPath() string {
-	return NormalizeLDConfigPath("@/sbin/ldconfig")
+// assertValid checks for a valid config.
+func (c *Config) assertValid() error {
+	err := c.NVIDIAContainerCLIConfig.Ldconfig.assertValid(c.Features.AllowLDConfigFromContainer.IsEnabled())
+	if err != nil {
+		return errors.Join(err, errInvalidConfig)
+	}
+	return nil
+}
+
+// getLdConfigPath allows us to override this function for testing.
+var getLdConfigPath = getLdConfigPathStub
+
+func getLdConfigPathStub() ldconfigPath {
+	return ldconfigPath("@/sbin/ldconfig").normalize()
 }
 
 func getUserGroup() string {